Thrust and Friction Example (2D)

[JeffM2501]

Showing how motion works using velocity, acceleration, and time.

#include "raylib.h"
#include "raymath.h"

int main(void)
{
    const int screenWidth = 1024;
    const int screenHeight = 1024;

    // setup raylib
    InitWindow(screenWidth, screenHeight, "thrust and friction");

    SetTargetFPS(155);
    
    Vector2 pos = { screenWidth * 0.5f, screenHeight * 0.5f };  // player position
    Vector2 velocity = { 0,0 };                                 // player speed ( in x and y )
    float friction = 200;                                       // friction ( in pixels per second )
    float maxSpeed = 400;                                       // max speed (in pixels per second )
    float thrust = 200;                                         // thrust acceleration ( in pixels per second per second )

    while (!WindowShouldClose())
    {
        Vector2 input = { 0 };

        // see what directions we want to go
        if (IsKeyDown(KEY_W))
            input.y -= 1;
        if (IsKeyDown(KEY_S))
            input.y += 1;
        if (IsKeyDown(KEY_A))
            input.x -= 1;
        if (IsKeyDown(KEY_D))
            input.x += 1;

        // add our input dir + thrust for this frame to our velocity
        velocity = Vector2Add(velocity, Vector2Scale(input, thrust * GetFrameTime()));

        // if we are not thrusting, we are applying friction
        if (Vector2LengthSqr(input) == 0)
        {
            // see how fast we are going
            float mag = Vector2Length(velocity);
            if (mag > 0)
            {
                // if we are going over 0, then slow us down by the friction for this frame
                mag -= friction * GetFrameTime();
                if (mag < 0)
                    mag = 0;    // we don't want to go backwards

                // set our new velocity vector based on the slowed down value
                velocity = Vector2Scale(Vector2Normalize(velocity), mag);
            }
        }
        else if (Vector2LengthSqr(velocity) > maxSpeed * maxSpeed) // see if we are going too fast
        {
            // if we are, clamp the speed to our max
            velocity = Vector2Scale(Vector2Normalize(velocity), maxSpeed);
        }

        // see see where we would go if we moved along the velocity for this frame
        Vector2 newPos = Vector2Add(pos, Vector2Scale(velocity, GetFrameTime()));

        // see if X is out of bounds
        if (newPos.x < 0 || newPos.x > GetScreenWidth())
        {
            // if so, use the old position
            newPos.x = pos.x;

            // and bounce us backwards in this axis
            velocity.x *= -1;
        }

        // see if Y is out of bounds
        if (newPos.y < 0 || newPos.y > GetScreenHeight())
        {
            // if so, use the old position
            newPos.y = pos.y;

            // and bounce us backwards in this axis
            velocity.y *= -1;
        }

        // update to our new position
        pos = newPos;

        // draw the scene
        BeginDrawing();
        ClearBackground(RAYWHITE);

        // draw the rectangle
        DrawRectangle(pos.x, pos.y, 25, 25, RED);

        DrawFPS(0, 0);
        DrawText(TextFormat("V x%f y%f", velocity.x, velocity.y), 0, 20, 20,  BLACK);

        EndDrawing();
    }
}